KR20140046081A - Cylindrical battery - Google Patents

Abstract

Provided is a small cylindrical battery which realizes both improvement of battery characteristics and improvement of long-term reliability and stability. The cylindrical battery includes a cylindrical bottomed cylindrical battery case 1, an electrode group 5 accommodated in the battery case 1 together with the electrolyte, a sealing member 8 fitted in the opening of the battery case 1, The opening of the battery case 1 is sealed by drawing the sealing member 8 and the gasket 9 interposed between the battery case 1 and the opening end of the battery case 1. The battery case 1 is made of stainless steel. The outer diameter of the battery case 1 is 10 mm or less, and the thickness of the battery case is 0.05 mm or more and 0.2 mm or less.

Description

Cylindrical Battery {CYLINDRICAL BATTERY}

The present invention relates to a cylindrical battery including a battery case such as a lithium ion secondary battery.

2. Description of the Related Art In recent years, lithium ion secondary batteries have been widely used as power sources for driving electronic devices in electronic devices such as portable digital devices. Particularly, in a portable device requiring a multifunctional and heavy load such as a smart phone, improvement of battery characteristics such as energy density and load characteristics and reduction in weight are required for the battery used as the power source. In addition, there is a demand for improvement in long-term reliability and safety.

The lithium ion secondary battery typically has a metal battery case to reduce the thickness of the battery case to increase the internal volume, while charging the battery case with the power generating element at a high density can improve the energy density. Thinning the thickness of the battery case is particularly effective for a small battery because it increases the internal volume. As another example, there is a lithium ion battery using a metal-resin laminate sheet instead of the battery case. In this case, by including the battery component such as the negative electrode, the separator, and the electrolytic solution by the thin sheet, the energy density is improved and the weight is reduced.

Patent Document 1: JP-A-2009-181754 Patent Document 2: JP-A-2008-223087 Patent Document 3: JP-A-2007-227339

However, it has been difficult to improve battery characteristics and improve long-term reliability and safety in batteries such as lithium ion secondary batteries. For example, iron, aluminum, or the like is generally used for a battery case material in a lithium ion secondary battery. Therefore, if the thickness of the metal plate constituting the battery case is reduced for the purpose of improving the energy density, the strength of the battery case is lowered. The lowering of the strength of the battery case results in a decrease in sealability or a decrease in tolerance to an increase in the internal pressure caused by expansion of the electrode plate or gas caused by repetition of charge and discharge cycles. As a result, deformation of the battery case and deterioration of battery characteristics are liable to occur, and it becomes difficult to realize long-term reliability.

In addition, when a metal-resin laminated sheet is used instead of the battery case, the energy density is improved, but the problem caused by the reduction in the strength of the battery case becomes apparent. For example, by repeating a typical charge / discharge cycle, gas is generated by the decomposition of the electrolytic solution, whereby the internal pressure is increased, and the battery remarkably expands. In addition, since the sealing property in the vicinity of the lead portion is weak, moisture tends to invade from the outside to the inside of the battery. For this reason, gas is generated by the moisture, which causes the internal pressure to rise and the battery to expand. Such swelling may destroy the seal by the laminate sheet.

As described above, it is very important to use a battery case and realize high strength and high sealing performance while reducing the thickness of the battery case, in order to achieve both improvement in battery characteristics and improvement in long-term reliability and safety.

There has been proposed a technique for increasing the strength of the battery case opening by thickening only the thickness of the opening portion of the battery case so as to obtain a high sealing property when the sealing member is fitted to the opening portion of the battery case (for example, 1). However, since such a battery case is complicated in shape, it is difficult to perform molding and quality control and is not suitable for mass production.

Further, a technique of using an aluminum alloy material whose strength is enhanced by addition of a dissimilar metal and heat treatment as a material of a battery case has been proposed (for example, see Patent Document 2). However, simply increasing the strength of the battery case reduces the workability of the battery case, making it difficult to achieve high sealing performance.

An object of the present invention is to provide a small cylindrical battery in which improvement of battery characteristics and improvement of long-term reliability and safety are realized.

The inventors of the present invention have found a condition in which the improvement of the battery characteristics and the improvement of the long-term reliability and the safety are compatible with each other in the small-sized cylindrical battery.

A cylindrical battery according to the present invention is a cylindrical battery comprising: an electrode group (electrode group) housed in a cylindrical battery cell case and a battery case together with an electrolyte; a sealing member sandwiched between openings of the battery case; And an opening of the battery case is sealed by drawing the end of the opening of the battery case. In addition, the battery case is made of stainless steel. The outer diameter of the battery case is 10 mm or less, and the thickness of the battery case is 0.05 mm or more and 0.2 mm or less.

According to the cylindrical battery of the present invention, it is possible to achieve both improvement in battery characteristics and improvement in long-term reliability and safety.

While the novel features of the invention are set forth in the appended claims, the invention will be better understood by reference to the following detailed description, taken in conjunction with the drawings, together with other objects and features of the invention, both as to organization and content.

1 is a longitudinal sectional view conceptually showing a cylindrical battery according to an embodiment of the present invention.

First, a cylindrical battery according to the present invention will be described.

A cylindrical battery according to the present invention comprises a cylindrical cylindrical battery case and an electrode group housed in the battery case together with an electrolyte, a sealing member sandwiched in an opening of the battery case, and a sealing member interposed between the sealing member and the battery case And the opening of the battery case is sealed by drawing the opening end of the battery case. In addition, the battery case is made of stainless steel. The outer diameter of the battery case is 10 mm or less, and the thickness of the battery case is 0.05 mm or more and 0.2 mm or less.

As shown in Table 1, stainless steel has a significantly higher tensile fracture strength than iron (Fe) or aluminum (Al). Table 1 shows SUS316L (austenitic stainless steel) as an example of stainless steel. Therefore, by using stainless steel as the material of the battery case as in the present invention, high strength of the battery case can be maintained even when the thickness of the battery case is made thin as a whole uniform. In addition, since stainless steel has high strength and excellent workability, high sealing performance is achieved in the battery case.

In addition, the inventors of the present invention have found that high sealing performance is realized in a small cylindrical battery having an outer diameter of 10 mm or less, especially when the thickness of the battery case is 0.05 mm or more and 0.2 mm or less. Further, the present inventors have found that these conditions are particularly preferable in a small cylindrical battery having an outer diameter of 6 mm or less of the battery case. As described above, when the opening of the battery case is sealed by drawing the opening end of the battery case in the small-sized cylindrical battery, the thickness of the battery case is very important as a condition for enhancing the sealing property.

When drawing is performed on the end of the opening of the battery case, the battery case shrinks (that is, the diameter of the battery case becomes smaller) at the tightened portion of the battery case. When the diameter of the battery case before the drawing process is 15 mm or more, the rate of shrinkage of the battery case 1 due to the drawing process is small, and the sealing property is not greatly affected. However, when the diameter of the battery case 1 before the drawing process is 10 mm or less, the rate of shrinkage of the battery case 1 due to the drawing process becomes large, and at the end of the opening of the battery case, And the like. Such a problem is conspicuous when the diameter of the battery case before drawing is 6 mm or less, and the sealing property is deteriorated. The inventors of the present invention have found that when the battery case 1 is made of stainless steel and the thickness of the battery case 1 is 0.05 mm or more and 0.2 Mm or less, a high sealing property can be realized.

When the cylindrical battery is a lithium ion battery, the battery case is preferably made of a material having a wide potential window and a high acid corrosion resistance. In this respect, stainless steel such as SUS316L is very strong against the reduction side (ring side) potential and has a potential window wider than iron or copper though not on the oxidation side. In addition, in the presence of lithium ions, aluminum is precipitated on the surface when a reducing potential is applied, thereby producing an alloy with lithium. Such an alloying reaction involves expansion of the volume. Therefore, when the battery case is made of aluminum, the battery case becomes brittle and its strength is lowered, and it is difficult to realize long-term reliability of the battery.

In addition, stainless steel has higher acid corrosion resistance than iron, copper and aluminum. This is because stainless steel has a protective layer on its surface. In a lithium ion battery, lithium hexafluorophosphate (LiPF ₆ ) is generally used as a supporting electrolyte. Such supporting electrolyte constitutes an electrolytic solution having high ion conductivity and can realize excellent load characteristics. On the other hand, lithium hexafluorophosphate hydrolyzes in the presence of water to generate hydrofluoric acid (HF), which is a strong acid. For this reason, in the lithium ion battery, it is important to increase the sealing property so as to suppress intrusion of moisture from the outside and increase the acid corrosion resistance of the battery case in realizing long-term reliability. This is because the corrosion of the battery case invites moisture intrusion, thereby accelerating the progress of corrosion.

Thus, with the cylindrical battery according to the present invention, it is possible to achieve both improvement in battery characteristics and improvement in long-term reliability and safety. Further, since the thickness of the battery case can be made uniform, the forming and quality control of the battery case is easy.

In a preferred specific construction of the cylindrical battery, the stainless steel constituting the battery case is an austenitic stainless steel having a low carbon content. The stainless steel constituting the battery case is preferably stainless steel having a carbon content of 0.08 mass% or less. In addition, the carbon content of the stainless steel is more preferably 0.05 mass% or less, and particularly preferably 0.03 mass% or less.

As shown in Table 1, the stainless steel having a small carbon content has a large elongation and a high tensile fracture strength. Therefore, stainless steel having a low carbon content has high workability. That is, when forming the battery case 1, it is easy to stretch the stainless steel and thinly process it, and the processing accuracy is high. For example, in an elongated cylindrical battery, a battery case having a large height-diameter ratio can be easily and highly precisely formed, for example, by deep drawing. Therefore, the battery case 1 having a thickness of 0.05 mm or more and 0.2 mm or less can be easily and highly precisely formed, and as a result, it is possible to stably manufacture a cylindrical battery having high sealing performance.

In another preferred specific construction of the cylindrical battery, the stainless steel constituting the battery case 1 is a stainless steel having a copper content of 1.0 mass% or more and 6.0 mass% or less. More preferably, the copper content is 1.5% by mass or more and 5.0% by mass or less. As described above, the stainless steel including copper has high tensile break strength, elongation and acid corrosion resistance, and has a small contact resistance on the stainless steel surface as shown in Table 2. The surface of the stainless steel usually has a protective layer for enhancing acid corrosion resistance. When copper is not contained in the stainless steel, this protective layer causes a large contact resistance. On the other hand, since copper is included in stainless steel, the resistance of the protective layer is reduced, and as a result, the contact resistance is reduced.

According to the stainless steel including copper, electrical contact with the device can be easily obtained without forming a new surface layer or a terminal. Further, by increasing the contact area with the electrodes in the battery, the internal resistance of the battery is reduced without welding the battery case and the electrode by welding or the like, and as a result, good load characteristics can be obtained.

As described above, stainless steel has high strength. Therefore, when the stainless steel is processed into a desired shape, a large force is required. Therefore, it is preferable that the battery case is formed into a user cylindrical shape by a deep drawing process of a thin stainless steel plate. Deep drawing processing makes it possible to form a battery case having a thin thickness and uniformity and a small variation in shape and thickness. In addition, when deep drawing is performed, loss of material is small. Therefore, in the cylindrical battery, it is possible to improve both the battery characteristics and the long-term reliability and safety.

As a method for machining stainless steel into a cylindrical shape, there are methods such as an impact press method and a DI (drawing & ironing) method. However, in these methods, it is necessary to uniformly apply a large force continuously in the process of forming, which is difficult to control, and therefore the shape and thickness of the battery case tend to be varied. Particularly, when the thickness of the battery case is reduced, a hole may be formed or cut. As a method for machining a stainless steel into a cylindrical shape, there is a method of cutting a columnar material. However, this method makes it difficult to cause variations in the shape of the battery case, but it is not efficient due to a large loss of the material.

Next, the embodiments of the present invention will be described concretely with reference to the drawings. The constitution of each part of the present invention is not limited to the embodiment, and various modifications can be made within the technical scope described in the claims.

1 is a longitudinal sectional view schematically showing a cylindrical battery according to an embodiment of the present invention. 1, the cylindrical battery includes a cylindrical cylindrical battery case 1, an electrode group 5 accommodated in the battery case 1 together with a non-aqueous electrolyte (non-aqueous electrolyte) A sealing member 8 sandwiched between the sealing member 8 and the battery case 1, and a gasket 9 interposed between the sealing member 8 and the battery case 1.

«Battery case»

The battery case 1 is formed by deep-drawing a stainless steel material having a uniform thickness. The outer diameter of the battery case 1 is 10 mm or less, particularly preferably 6 mm or less. The thickness of the battery case 1 is 0.05 mm or more and 0.2 mm or less. The ratio of the thickness (side face) of the side wall of the battery case 1 to the thickness of the bottom (back) is 0.20 or more and 1.20 or less, preferably 0.33 or more and 1.05 or less.

The stainless steel constituting the battery case (1) is preferably an austenitic stainless steel having a small carbon content. The stainless steel constituting the battery case 1 is preferably stainless steel having a carbon content of 0.08 mass% or less. The carbon content of the stainless steel is more preferably 0.05 mass% or less, and particularly preferably 0.03 mass% or less.

The stainless steel constituting the battery case 1 preferably contains copper. In such a battery case 1, the content of copper is preferably 1.0 mass% or more and 6.0 mass% or less, and particularly preferably 1.5 mass% or more and 5.0 mass% or less.

&Quot; Sealing member and gasket "

The sealing member 8 and the gasket 9 seal the opening of the battery case 1. Specifically, the sealing member 8 and the gasket 9 are inserted into the opening of the battery case 1 so that the gasket 9 is interposed between the sealing member 8 and the battery case 1. Then, the end of the opening of the battery case 1 is drawn and engaged with the sealing member 8. Therefore, the gasket 9 is in tight contact with the side surface of the sealing member 8 and the inner surface of the battery case 1 in a compressed state. Thus, the opening of the battery case 1 is sealed. In the sealing member 8, a protruding portion exposed to the outside of the battery case 1 is fitted with a circular hole 11 made of an electrically insulating material. This disk 11 prevents electrical short-circuiting between the sealing member 8 and the battery case 1.

As the material of the gasket 9, polypropylene (PP), polyethylene (PE), polyphenylene sulfide (PPS), perfluoroalkylethylene-hexafluoropropylene copolymer (PFA) Is used. Particularly, PFA is preferable because it has a low moisture permeability and can inhibit the penetration of moisture into the inside of the battery, which can advance deterioration of the lithium ion battery.

«Electrode group»

The electrode group 5 has a negative electrode plate 2, a positive electrode plate 3 and a separator 4. In the electrode group 5, the negative electrode plate 2 and the positive electrode plate 3 are overlapped and wound together with the separator 4 interposed therebetween. The winding ends of at least one of the negative electrode plate 2 and the positive electrode plate 3 are fixed to the outer peripheral surface of the electrode group 5 by the fixing tape so as not to cause a deviation in the winding state of the electrode group 5. [ The electrode group 5 is housed in the battery case 1 together with a nonaqueous electrolyte (not shown). By the electrode group 5 as described above, the reaction area becomes large, and the strong load characteristic can be realized.

The negative electrode plate 2 and the positive electrode plate 3 are each composed of a core material which is a current collector and a composite layer (including an active material) formed on the surface of the core material . In order to increase the battery capacity, the compound layer is formed on the surface of the core material in a compressed state. Therefore, if the radius of the winding start portion of the negative electrode plate 2 and the positive electrode plate 3 in the electrode group 5 is too small, the composite layer is peeled off from the core material, Short circuit (internal short circuit) may occur. On the other hand, if the radius of the winding start portion is too large, the amount of the active material stored in the battery case 1 decreases, and the battery capacity becomes small. Therefore, it is necessary to start winding the negative electrode plate 2 and the positive electrode plate 3 with a proper radius. For example, in the case where the negative electrode plate 2 and the positive electrode plate 3 are wound by using a crimper, the diameter R of the winding core is preferably 0.6 mm or more and 3.0 mm or less, more preferably 0.8 mm or more and less than 1.5 mm, desirable. In the vicinity of the central axis of the electrode group 5, there is a space in which the active material does not exist. The space preferably has a diameter of 3.0 mm or less and particularly preferably a diameter of less than 1.5 mm.

The negative electrode lead 6 is electrically connected to the negative electrode plate 2 (specifically, a negative electrode core member to be described later) and the end portion of the negative electrode lead 6 is welded to the inner surface of the side wall of the battery case 1, Respectively. Further, when the stainless steel constituting the battery case 1 includes copper, the negative electrode lead 6 may be simply brought into contact with the inner surface of the side wall of the battery case 1. The negative electrode plate 2 is thus electrically connected to the battery case 1, and the battery case 1 functions as a negative electrode terminal. As the material of the negative electrode lead 6, for example, nickel, iron, stainless steel, copper or the like is used. The shape of the negative electrode lead 6 is not limited to a specific shape but may be a rectangular shape having a welding margin with the negative electrode core material and a welding margin with the battery case 1, An ellipse or a polygon in contact with a rectangle. The thickness of the negative electrode lead 6 is preferably 10 탆 or more and 120 탆 or less, particularly preferably 20 탆 or more and 80 탆 or less.

The positive electrode lead 7 is electrically connected to the positive electrode plate 3 (specifically, a positive electrode core member to be described later), and the end portion of the positive electrode lead 7 is bonded to the sealing member 8 by spot welding or the like . Thus, the positive electrode plate 3 is electrically connected to the sealing member 8, and the sealing member 8 functions as a positive electrode terminal. As the material of the positive electrode lead 7, for example, aluminum is used. The positive electrode lead 7 has a characteristic of curving at a small pressure, and although it does not have a particularly limited shape, it can be a rectangular shape or the like. The thickness of the cathode lead 7 is preferably 40 占 퐉 or more and 150 占 퐉 or less, more preferably 50 占 퐉 or more and 100 占 퐉 or less.

A ring-shaped intermediate member 10 made of an electrically insulating material is disposed between the electrode group 5 and the sealing member 8. The positive electrode lead 7 passes through the inside of the intermediate member 10, And is connected to the positive electrode plate 3 and the sealing member 8. This prevents the intermediate member 10 from electrically shorting between the cathode and the anode.

<Negative plate>

The negative electrode plate 2 is composed of a negative electrode core material which is a negative electrode collector and a negative electrode material mixture layer which is formed on the surface of the negative electrode core material. The negative electrode plate 2 is formed, for example, by depositing a negative electrode active material on the surface of the negative electrode core material in a thin film state. The negative electrode core member is a metal foil. The negative electrode core member is, for example, a long conductive substrate having a porous structure or a nonporous structure. As the material of the negative electrode core material, for example, stainless steel, nickel, copper, or the like is used. The thickness of the negative electrode core material is not particularly limited, but is preferably 1 탆 or more and 500 탆 or less, particularly preferably 5 탆 or more and 20 탆 or less. With the negative electrode core material having such a thickness, it is possible to reduce the weight of the negative electrode plate 2 while maintaining the strength of the negative electrode plate 2.

The negative electrode material mixture layer contains a negative electrode active material. The negative electrode active material will be described in detail below. It is preferable that the negative electrode material mixture layer contains a binder and the like in addition to the negative electrode active material.

(Negative electrode active material)

As the negative electrode active material, a material capable of absorbing and releasing lithium ions is used. Examples of such an anode active material include metals, metal fibers, carbon materials, oxides, nitrides, silicon compounds, tin compounds, and various alloying materials. Specific examples of the carbon material include various natural graphite, coke, graphitized carbon, carbon fiber, spherical carbon, various artificial graphite or amorphous carbon, and the like. .

Since a single substance such as silicon (Si) or tin (Sn) or a silicon compound or a tin compound has a large capacity density, it is preferable to use silicon, tin, silicon compound, or tin compound as the negative electrode active material desirable. Specific examples of the silicon compound include SiOx (0.05 <x <1.95) or B, Mg, Ni, Ti, Mo, Co, Ca, Cr, Cu, Fe, Mn, Nb, Ta, V, , C, N and Sn A silicon alloy in which a part of Si is substituted with at least one kind of element selected from the group of elements to be formed, or a silicon solid solution. Specific examples of the tin compound include Ni ₂ Sn ₄ , Mg ₂ Sn, SnOx (where 0 <x <2), SnO ₂ , or SnSiO ₃ . As the negative electrode active material, one of the above-listed negative electrode active materials may be used alone, or two or more of them may be used in combination.

<Positive plate>

The positive electrode plate 3 is composed of a positive electrode core material which is a positive electrode collector and a positive electrode material mixture layer formed on the surface of the positive electrode core material. The anode core member is a metal foil. As the anode core member, for example, a long conductive substrate having a porous structure or a nonporous structure is used. As the material of the anode core material, for example, aluminum or the like is used. The thickness of the positive electrode core material is not particularly limited, but is preferably 8 占 퐉 or more and 25 占 퐉 or less, more preferably 10 占 퐉 or more and 15 占 퐉 or less. By the positive electrode core having such a thickness, it is possible to constitute the electrode group 5 having a small diameter which is curved smoothly.

The positive electrode mixture layer includes a positive electrode active material, a binder, and a conductive agent. Here, the cathode active material, the binder and the conductive agent will be described in detail below.

(Cathode active material)

The cathode active material is preferably a lithium-containing complex oxide, and examples thereof include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiCo _x Ni _{1 - x} O ₂ , LiCo _x M _{1 - x} O ₂ , LiNi _x M _{1 - x} O _{2 , LiNi 1/3 Co 1/} 3 Mn 1/3 O 2, LiMn 2 O 4, LiMnMO 4, LiMePO 4, Li 2 MePO 4 F ( However, M is Na, Mg, Sc, Y, Mn, Fe, Co Mn, at least one of Ni, Cu, Zn, Al, Cr, Pb, Sb and B. x is 0 & ), And a case in which some elements of the lithium-containing compounds are substituted with different kinds of elements. As the cathode active material, a cathode active material surface-treated with a metal oxide, lithium oxide, or a conductive agent may be used. The surface treatment includes, for example, a hydrophobic treatment.

The average particle diameter of the positive electrode active material is preferably 5 占 퐉 or more and 20 占 퐉 or less. If the average particle diameter of the positive electrode active material is less than 5 mu m, the surface area of the active material particles becomes very large. As a result, the amount of the binder for obtaining the bonding strength that enables handling of the positive electrode plate 3 becomes extremely large. As a result, the amount of active material in the vicinity of the electrode plate decreases and the capacity decreases. On the other hand, if it exceeds 20 탆, a coating stalk is liable to be generated when the positive electrode material mixture slurry is applied to the positive electrode core material.

(Binder)

Examples of the binder include PVDF, polytetrafluoroethylene, polyethylene, polypropylene, an aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polyacrylic acid methyl ester, A polyacrylic acid ester, a polyacrylic acid ester, a polyacrylic acid hexyl ester, a polymethacrylic acid, a polymethacrylic acid methyl ester, a polymethacrylic acid ethyl ester, a polymethacrylic acid hexyl ester, a polyvinyl acetate, a polyvinylpyrrolidone, Hexafluoro polypropylene, styrene butadiene rubber, and carboxymethyl cellulose. Or a 2-membered ring selected from tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, A copolymer obtained by copolymerizing two or more kinds of materials, or a mixture obtained by mixing two or more selected materials.

Among the binders listed above, in particular, PVDF and its derivatives are chemically stable in the non-aqueous electrolyte secondary battery, and the positive electrode active material and the positive electrode active material constituting the positive electrode mixture layer are sufficiently bonded to the positive electrode material mixture layer and the positive electrode core material, Since the binder and the conductive agent are sufficiently bonded, good charge-discharge cycle characteristics and discharge performance can be obtained. For this reason, it is preferable to use PVDF or a derivative thereof as the binder of the present embodiment. Moreover, PVDF and its derivative are preferable in terms of cost since they are inexpensive. In the case of producing a positive electrode using PVDF as a binder, for example, when PVDF is dissolved in N-methylpyrrolidone or when PVDF in powder form is dissolved in a positive electrode mixture slurry .

(Conductive agent)

Examples of the conductive agent include graphites such as natural graphite or artificial graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black or thermal black, carbon fibers or metals Metal powders such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, and organic conductive materials such as phenylene derivatives.

<Separator>

As the separator 4, a microporous membrane, a woven fabric, or a nonwoven fabric having a large ion permeability and having a predetermined mechanical strength and electrical insulation property is used. Particularly, as the material of the separator 4, for example, polyolefin such as polypropylene or polyethylene is preferably used. Since the polyolefin is excellent in durability and has a shutdown function, the safety of the lithium ion secondary battery can be improved.

The thickness of the separator 4 is generally 10 mu m or more and 300 mu m or less, preferably 10 mu m or more and 40 mu m or less. The thickness of the separator 4 is more preferably 15 占 퐉 or more and 30 占 퐉 or less, particularly preferably 10 占 퐉 or more and 25 占 퐉 or less. When the microporous film is used as the separator 4, the microporous film may be a single layer film made of one kind of material or a composite film or multilayer film made of one kind or two or more kinds of materials. The porosity of the separator 4 is preferably 30% or more and 70% or less, more preferably 35% or more and 60% or less. Here, the porosity represents the ratio of the total volume of the pores to the total volume of the separator 4. [

<Non-aqueous electrolyte>

As the non-aqueous electrolyte contained in the battery case 1, a non-aqueous electrolyte in a liquid, gel, or solid state can be used. The liquid non-aqueous electrolyte includes an electrolyte salt (for example, a lithium salt) and a nonaqueous solvent for dissolving the electrolyte salt. The non-aqueous electrolyte in the gel state includes a non-aqueous electrolyte and a polymer material that retains the non-aqueous electrolyte. Examples of the polymer material include polyvinylidene fluoride, polyacrylonitrile, polyethylene oxide, polyvinyl chloride, polyacrylate, polyvinylidene fluoride hexafluoropropylene, and the like. The solid state nonaqueous electrolyte contains a polymer solid electrolyte.

The non-aqueous solvent and the electrolyte salt contained in the liquid non-aqueous electrolyte will be described in detail below.

(Non-aqueous solvent)

As the non-aqueous solvent for dissolving the electrolytic salt, a known non-aqueous solvent may be used. The kind of the nonaqueous solvent is not particularly limited, and for example, a cyclic carbonic ester, a chain carbonic ester, a cyclic carbonic acid ester, or the like is used. Specific examples of cyclic carbonic acid esters include propylene carbonate (PC) and ethylene carbonate (EC). Specific examples of the chain carbonic ester include diethyl carbonate (DEC), ethylmethyl carbonate (EMC), dimethyl carbonate (DMC), and the like. Specific examples of the cyclic carboxylic acid ester include gamma-butyrolactone (GBL) and gamma-valerolactone (GVL). As the non-aqueous solvent, one of the non-aqueous solvents listed above may be used alone, or two or more of them may be used in combination.

(Electrolytes)

Examples of the electrolyte salt to be dissolved in the nonaqueous solvent include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiB ₁₀ Cl ₁₀ , Lithium carbonate, LiCl, LiBr, LiI, chloropolan lithium, boric acid salts, imide salts and the like are used. Specific examples of the borate salts include bis (1, 2-benzenedioate (2) -O, O ') lithium borate, bis (2, 3-naphthalene dioate (2 -) - O, O ') lithium borate or bis (5-fluoro-2-orate-1-benzenesulfonic acid-O, O') boric acid Lithium, and the like. Specific examples of the imide salts include imidolithium ((CF ₃ SO ₂ ) ₂ NLi), barium trifluoromethanesulfonate imidolium phosphate (LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ )) or bispentafluorooctanesulfonic acid imide lithium ((C ₂ F ₅ SO ₂ ) ₂ NLi). As the electrolytic salts, one of the electrolytic salts listed above may be used alone, or two or more kinds of electrolytic salts may be used in combination.

The dissolution amount of the electrolyte salt in the non-aqueous solvent is preferably 0.5 mol / m 3 or more and 2 mol / m 3 or less.

The liquid non-aqueous electrolyte may contain, in addition to the electrolyte salt and the non-aqueous solvent, for example, an additive which decomposes on the negative electrode to form a film having a high lithium ion conductivity and increase the charging / discharging efficiency of the battery. Examples of additives having such a function include vinylene carbonate (VC), 4-methylvinylene carbonate, 4,5-dimethylvinylene carbonate, 4-ethylvinylene carbonate, 4,5-diethyl Vinylbenzene carbonate, vinylene carbonate, vinylene carbonate (VEC), or a mixture of two or more of vinylene carbonate, vinylene carbonate, Divinylethylene carbonate, and the like. As the additive, one of the additives listed above may be used alone, or two or more of them may be used in combination. Particularly, among the additives listed above, at least one selected from vinylene carbonate, vinylethylene carbonate and divinylethylene carbonate is preferable. The additive may also be such that a part of the hydrogen atoms of the additives listed above are substituted with fluorine atoms.

The liquid non-aqueous electrolyte may contain, in addition to the electrolyte salt and the non-aqueous solvent, for example, a known benzene derivative which decomposes upon overcharging to form a film on the electrode and deactivates the battery. As the benzene derivative having such functions, it is preferable to have a phenyl group and a cyclic compound group (ring compound group) adjacent to the phenyl group. Specific examples of the benzene derivative include cyclohexylbenzene, biphenyl, diphenyl ether, and the like. Specific examples of the cyclic compound group contained in the benzene derivative include a phenyl group, a cyclic ether group, a cyclic ester group, a cycloalkyl group, and a phenoxy group. As the benzene derivative, one of the benzene derivatives listed above may be used alone, or two or more kinds of benzene derivatives may be used in combination. However, the content of the benzene derivative in the non-aqueous solvent is preferably 10 vol% or less of the non-aqueous solvent.

Example

Hereinafter, embodiments of the present invention will be described in detail.

&Lt; Example 1 &gt;

(Preparation of positive electrode plate)

As the cathode active material, LiNi ₀ . ₈₂ Co ₀ . ₁₅ Al ₀ . ₀₃ O ₂ was prepared. As the binder, 4.7 vol% of PVDF was prepared for 100 vol% of the cathode active material. As the conductive agent, acetylene black of 4.5 vol% was prepared for 100 vol% of the positive electrode active material. Further, N-methylpyrrolidone (NMP) was prepared as a solvent, and the prepared binder was dissolved in the solvent to prepare a solution. Then, the prepared cathode active material, the conductive agent, and the solution were mixed to prepare a cathode mixture slurry.

Next, an aluminum foil having a thickness of 15 mu m was prepared as the anode core material, and the anode mixture slurry was applied to both surfaces of the aluminum foil, followed by drying. Subsequently, the positive electrode core material coated with the positive electrode material mixture slurry on both sides and rolled was rolled to produce a 0.12 mm thick plate-shaped positive electrode plate. The positive electrode plate was cut to a width of 30.5 mm and a length of 19.0 mm to produce a positive electrode plate 3 having a thickness of 0.12 mm, a width of 30.5 mm and a length of 19.0 mm.

(Preparation of negative electrode plate)

As the negative electrode active material, a graphite graphite having an average particle diameter of 20 mu m was prepared. As the binder, 4.7 vol% of SBR was prepared for 100 vol% of the negative electrode active material. As the conductive agent, 4.5% by volume of acetylene black was prepared with respect to 100% by volume of the negative electrode active material. Pure water was prepared as a solvent, and a binder prepared in this solvent was dissolved to prepare a solution. Then, the prepared negative electrode active material, the conductive agent and the solution were mixed to prepare a negative electrode mixture slurry.

Next, a copper foil having a thickness of 8 占 퐉 was prepared as a negative electrode core material, and an anode mixture slurry was applied to both surfaces of the copper foil, followed by drying. Thereafter, the negative electrode core material coated / dried with the negative electrode material mixture slurry on both sides was rolled to produce a 0.15 mm thick plate-like negative electrode plate. The negative electrode plate was cut to a width of 29.5 mm and a length of 37.0 mm to prepare a negative electrode plate 2 having a thickness of 0.15 mm, a width of 29.5 mm and a length of 37.0 mm.

(Preparation of non-aqueous electrolyte)

As a non-aqueous solvent, a mixed solvent in which ethylene carbonate and dimethyl carbonate were mixed was prepared so that the volume ratio was 1: 3. LiPF ₆ was prepared as an electrolyte salt. Then, 5 wt% of vinylene carbonate was added as an additive for increasing the charging / discharging efficiency of the battery, and LiPF ₆ , an electrolytic salt, was dissolved in the prepared nonaqueous solvent so that the molar concentration with respect to the nonaqueous solvent was 1.4 mol / Thus, a non-aqueous electrolyte was prepared.

(Production of cylindrical battery)

First, a positive electrode lead 7 made of aluminum was attached to the positive electrode core 3 of the prepared positive electrode plate 3 and the negative electrode lead 6 made of nickel was attached to the negative electrode core material of the prepared negative plate 2, The positive electrode plate 3 was wound with a separator 4 made of polyethylene (with a thickness of 16 m) interposed therebetween. Thus, an electrode group 5 was produced. Further, a battery case 1 having a thickness of 0.1 mm and an outer diameter of 3.5 mm was produced using SUS316L (an austenitic stainless steel containing no copper and having a carbon content of 0.03 mass% or less).

Next, the intermediate member 10 is disposed on the upper end of the electrode group 5. Then, the cathode lead 6 was welded to the battery case 1, and the cathode lead 7 was welded to the sealing member 8. Then, the electrode assembly 5 was housed in the battery case 1. Thereafter, the nonaqueous electrolyte was injected into the battery case 1 by the pressure reducing method. Thereafter, a sealing member 8 and a gasket 9 made of PFA were inserted into the opening of the battery case 1 so that the gasket 9 was interposed between the battery case 1 and the sealing member 8 . Then, the end of the opening of the battery case 1 was engaged with the sealing member 8 to produce a cylindrical battery having a diameter of 3.5 mm and a height of 35 mm. This cylindrical battery is referred to as the first embodiment.

&Lt; Example 2 &gt;

As the stainless steel constituting the battery case 1, an austenitic stainless steel having a copper content of 3.80 mass% was used. The other manufacturing conditions are the same as in the first embodiment. The cylindrical battery thus fabricated was the second embodiment.

&Lt; Example 3 &gt;

SUS316L was used as the material of the battery case 1, and the thickness of the battery case 1 (outer diameter 3.5 mm) was set to 0.15 mm. The other manufacturing conditions are the same as in the first embodiment. The cylindrical battery thus fabricated was the third embodiment.

<Example 4>

As the material constituting the battery case 1, SUS316L was used, and the thickness of the battery case 1 (outer diameter 3.5 mm) was set to 0.20 mm. The other manufacturing conditions are the same as in the first embodiment. The cylindrical battery thus fabricated was Example 4.

&Lt; Comparative Example 1 &

SUS316L was used as a material constituting the battery case 1, and the thickness of the battery case 1 (outer diameter 3.5 mm) was set to 0.25 mm. The other manufacturing conditions are the same as in the first embodiment. The cylindrical battery thus produced was used as Comparative Example 1.

&Lt; Comparative Example 2 &

Iron (Fe) was used as a material constituting the battery case 1 (thickness 0.1 mm, outer diameter 3.5 mm). The other manufacturing conditions are the same as in the first embodiment. The cylindrical battery thus produced was designated as Comparative Example 2.

&Lt; Comparative Example 3 &

Iron (Fe) was used as a material for constituting the battery case 1, and the thickness of the battery case 1 (outer diameter 3.5 mm) was set to 0.2 mm. The other manufacturing conditions are the same as in the first embodiment. The cylindrical battery thus produced was designated as Comparative Example 3.

The cylindrical batteries of Examples 1 to 4 and the cylindrical batteries of Comparative Examples 1 to 3 were each fabricated in five, and the average value of the energy density, the liquid leakage occurrence rate, and the internal short generation rate were determined for these cylindrical batteries. These results are shown in Table 3. Incidentally, the rate of occurrence of the internal short is a rate of occurrence of shot when a stress of 1.5 kgf is applied to the side surface of a cylindrical battery with the end of a round bar having a diameter of 1.0 mm resting on the side.

The cylindrical batteries of Examples 1 to 4 and the cylindrical batteries of Comparative Examples 1 to 3 were further subjected to a long-term reliability test. Specifically, these cylindrical batteries were stored for 20 days in an atmosphere of 85 ° C-90% RH, and then the rate of expansion of the battery case 1 and the rate of retention of the battery capacity were obtained. The rate of increase in the outer diameter of the battery case 1 was obtained as the expansion rate of the battery case 1. [ The retention rate of the battery capacity was obtained based on the initial battery capacity. These results are shown in Table 4.

Comparing Examples 1 to 4 and Comparative Example 1 in Table 3 shows that the energy density is lower in Comparative Example 1 in which the thickness of the battery case 1 is thicker and the energy density is greater as the thickness of the battery case 1 is thinner I found out. This is because, as the thickness of the battery case 1 becomes thinner, the inner volume of the battery case 1 (in which the power generating element is housed) becomes larger.

In Table 3 and Table 4, although the thickness of the battery case 1 was 0.10 mm, the following differences were found by comparing Example 1 with Comparative Example 2. That is, in Comparative Example 2 where the material of the battery case 1 was iron, internal short-circuiting easily occurred and the battery case 1 was easy to expand. In Example 1 in which the material of the battery case 1 was SUS316L, A short circuit did not occur and the battery case 1 did not expand. This is because the strength of SUS316L is higher than that of iron (Fe), and thus the strength of the battery case 1 constructed of SUS316L is increased. It can be considered that the expansion of the battery case 1 in Comparative Example 2 is caused by the generation of hydrogen gas due to the influence of moisture penetrated into the battery case.

Comparison of Examples 1 to 4 and Comparative Example 1 in Table 3 reveals that Comparative Example 1 in which the thickness of the battery case 1 is 0.25 mm is obtained even though the material of the battery case 1 is SUS 316L and the outer diameter is the same, It is easy for liquid leakage to occur, whereas in Examples 1 to 4 in which the thickness is 0.20 mm or less, liquid leakage does not occur. That is, in Examples 1 to 4, high sealing performance can be realized. This is because, in Examples 1 to 4, no abnormal shape such as low roundness or wrinkles is generated, and therefore, a path for causing liquid leakage is not formed.

Comparing Examples 1 to 4 and Comparative Example 1 in Table 4 shows that although the battery case 1 is made of SUS 316L in the same material, in Comparative Example 1 in which the thickness of the battery case 1 is 0.25 mm, Whereas in Examples 1 to 4 where the thickness is 0.20 mm or less, the capacity retention rate is increased to 50% or more. This is because abnormal shapes such as low roundness and wrinkles do not occur in Examples 1 to 4, and evaporation of electrolytic solution and invasion of moisture from the outside are suppressed.

On the other hand, in Comparative Examples 2 and 3 in which the material of the battery case 1 was Fe (Fe), the capacity retention rate was remarkably low. This is because the strength of the battery case 1 is low and therefore the battery case 1 is liable to expand with the generation of hydrogen gas and therefore the sealing property (see the leakage leakage rate in Table 3) Because. It is also conceivable that the cell case is corroded by the generation of hydrofluoric acid, which is a strong acid, and that the corrosion causes invasion of moisture and accelerates the progress of corrosion, so that high battery capacity can not be maintained.

Comparing Example 1 and Example 2 in Tables 3 and 4, it can be seen that even if the stainless steel constituting the battery case 1 contained copper, it was found that the copper did not adversely affect battery characteristics and long-term reliability . Further, copper contained in stainless steel lowers the contact resistance of the surface of stainless steel.

From these results, the following can be seen. That is, in order to increase the strength of the battery case 1, it is preferable to use stainless steel as the material of the battery case 1. [ As a result, the internal short circuit is less likely to occur. In addition, by setting the thickness of the battery case 1 to 0.2 mm or less, the energy density is improved and the sealing property and the capacity retention ratio are improved. As a result, improvement in battery characteristics and improvement in long term reliability and safety are both achieved.

&Lt; Example 5 &gt;

SUS316L was used as the material for constituting the battery case 1, and the outer diameter of the battery case 1 (0.1 mm in thickness) was 6 mm. The other manufacturing conditions are the same as in the first embodiment. The cylindrical battery thus fabricated was Example 5.

<Example 6>

SUS316L was used as a material constituting the battery case 1, and the outer diameter of the battery case 1 (0.1 mm in thickness) was 10 mm. The other manufacturing conditions are the same as in the first embodiment. The cylindrical battery thus fabricated was Example 6.

&Lt; Comparative Example 4 &

As the material constituting the battery case 1, SUS316L was used, and the outer diameter of the battery case 1 (0.1 mm in thickness) was 15 mm. The other manufacturing conditions are the same as in the first embodiment. The cylindrical battery thus produced was designated as Comparative Example 4. [

&Lt; Comparative Example 5 &

As the material constituting the battery case 1, SUS316L was used, and the thickness of the battery case 1 was 0.2 mm and the outside diameter was 15 mm. The other manufacturing conditions are the same as in the first embodiment. The cylindrical battery thus produced was designated as Comparative Example 5.

&Lt; Comparative Example 6 &gt;

Iron (Fe) was used as a material for constituting the battery case 1, and the outer diameter of the battery case 1 (0.1 mm in thickness) was 6 mm. The other manufacturing conditions are the same as in the first embodiment. The cylindrical battery thus produced was designated as Comparative Example 6.

&Lt; Comparative Example 7 &

Iron (Fe) was used as a material for constituting the battery case 1, and the outer diameter of the battery case 1 (thickness 0.1 mm) was 10 mm. The other manufacturing conditions are the same as in the first embodiment. The cylindrical battery thus produced was designated as Comparative Example 7.

&Lt; Comparative Example 8 &gt;

Iron (Fe) was used as a material constituting the battery case 1, and the outer diameter of the battery case 1 (0.1 mm in thickness) was 15 mm. The other manufacturing conditions are the same as in the first embodiment. The cylindrical battery thus produced was designated as Comparative Example 8.

&Lt; Comparative Example 9 &

The battery case 1 was made of iron (Fe), and the battery case 1 had a thickness of 0.2 mm and an outer diameter of 15 mm. The other manufacturing conditions are the same as in the first embodiment. The cylindrical battery thus produced was designated as Comparative Example 9.

Five cylindrical batteries of Examples 1, 5 and 6 and cylindrical batteries of Comparative Examples 2 and 4 to 9 were fabricated, and the liquid leakage occurrence rate, internal shortage occurrence rate and cell capacity retention rate of these cylindrical batteries were obtained. These results are shown in Table 5. The rate of occurrence of the internal short is a rate of occurrence of shot when a stress of 1.5 kgf is applied while the end of a round bar having a diameter of 1.0 mm is pressed against the side surface of the cylindrical battery. The retention ratio of the battery capacity was obtained after the cylindrical battery was stored for 20 days under an atmosphere of 85 ° C-90% RH. The retention rate of the battery capacity was obtained based on the initial battery capacity.

By comparing Examples 1, 5 and 6 and Comparative Example 4 in Table 5, the following differences were found although the material of the battery case 1 was the same SUS 316L and the thickness was 0.10 mm. That is, in Comparative Example 4 in which the outer diameter of the battery case 1 was 15 mm, an internal short circuit tended to occur easily. On the other hand, in Examples 1, 5, and 6 in which the outer diameter was 10 mm or less, I did. This is for the following reason. That is, even when the battery case 1 is constituted by the high-strength SUS316L, the curvature of the side surface of the battery case 1 becomes small when the outer diameter of the battery case 1 is large, The case 1 is easily deformed. On the other hand, if the outer diameter of the battery case 1 is small, the curvature of the side surface of the battery case 1 becomes large, and as a result, the battery case 1 becomes difficult to deform with respect to external force.

On the other hand, in Comparative Examples 2 and 6 to 8 where the material of the battery case 1 is iron (Fe), the rate of occurrence of internal short was remarkably high. This is because the strength of the battery case 1 is low and therefore the battery case 1 is easily deformed with respect to an external force. In Comparative Examples 2 and 6 to 8, since the strength of the battery case 1 was low, leakage of liquid easily occurred. In Comparative Examples 2 and 6 to 8, the capacity retention rate was remarkably low. This is because the strength of the battery case 1 is low, so that the battery case 1 is easily expanded with the generation of hydrogen gas, and thus the sealing property is lowered, but the battery characteristics are deteriorated. In addition, it is also conceivable that the cell case is corroded by the generation of hydrofluoric acid, which is a strong acid, and the corrosion causes invasion of moisture and accelerates the progress of corrosion, so that it is impossible to maintain a high battery capacity.

From these results, the following can be found. That is, in order to increase the strength of the battery case 1, it is preferable to use stainless steel as the material of the battery case 1. [ As a result, the internal short circuit is less likely to occur. In addition, by setting the outer diameter of the battery case 1 to 10 mm or less, the sealability and the capacity retention rate are improved. As a result, the battery characteristics are improved and the long-term reliability and safety are improved. It is also understood from the results of Comparative Examples 5 and 9 that the thickness of the battery case 1 is increased irrespective of the material of the battery case 1 when the outer diameter of the battery case 1 is large , Long-term reliability and safety are improved. However, when the outer diameter of the battery case 1 is small (10 mm or less), when the thickness of the battery case 1 is increased, the degradation of the inner volume becomes remarkable and the sealing by drawing processing becomes difficult, .

<Example 7>

SUS316 (austenitic stainless steel having a carbon content of 0.08 mass% or less) was used as the material constituting the battery case 1. [ The other manufacturing conditions are the same as in the first embodiment. The cylindrical battery thus fabricated was Example 7.

<Comparative Example 10>

As the material constituting the battery case 1, SUS430 (ferritic stainless steel having a carbon content of 0.12% by mass or less) was used. The other manufacturing conditions are the same as in the first embodiment. The cylindrical battery thus produced was referred to as Comparative Example 10.

Five cylindrical batteries of Examples 1 and 7 and five cylindrical batteries of Comparative Example 10 were produced, respectively, and liquid leakage occurrence rates and battery capacity retention rates were determined for these cylindrical batteries. These results are shown in Table 6. The battery capacity retention rate was obtained after the cylindrical battery was stored for 20 days under an atmosphere of 85 ° C-90% RH. In addition, the retention rate of the battery capacity was obtained based on the initial battery capacity.

From the results shown in Table 6, it can be seen that in Examples 1 and 7 in which the carbon content is 0.08 mass% or less, liquid leakage hardly occurs and the capacity retention rate is high. It is understood that a more preferable carbon content is 0.03 mass% or less.

As shown in Table 1, the stainless steel having a small carbon content has a large elongation and a high tensile fracture strength. Therefore, stainless steel having a low carbon content has high workability. That is, when the battery case 1 is formed, it is easy to stretch the stainless steel to be thin, and the processing accuracy is high. Therefore, the battery case 1 having a small thickness can be easily formed with high accuracy, and as a result, it is possible to stably manufacture a cylindrical battery having high sealing performance.

From this result, the following can be known. That is, the stainless steel constituting the battery case is preferably a stainless steel having a carbon content of 0.08 mass% or less, and particularly preferably a stainless steel having a carbon content of 0.03 mass% or less. As a result, the sealing property and the capacity retention ratio are improved, and as a result, the improvement of the battery characteristics and the improvement of the long-term reliability and safety are both achieved.

&Lt; Example 8 &gt;

A cylindrical battery was manufactured under the condition that the negative electrode lead 6 was simply brought into contact with the battery case 1 without welding in the second embodiment. Other manufacturing conditions are the same as in the second embodiment. The cylindrical battery thus fabricated was Example 8.

<Example 9>

In Example 1, a cylindrical battery was produced under the condition that the negative electrode lead 6 was simply brought into contact with the battery case 1 without welding. The other manufacturing conditions are the same as in the first embodiment. The cylindrical battery thus fabricated was Example 9.

The internal resistance of the cylindrical batteries of Examples 8 and 9 was determined. The results are shown in Table 7.

From the results shown in Table 7, when the negative electrode lead 6 was simply brought into contact with the battery case 1, the internal resistance was remarkably increased in Example 9 containing no copper, whereas in Example 8 containing copper The internal resistance is remarkably reduced. That is, it is found that the contact resistance on the surface of the stainless steel is reduced by mixing copper in the austenitic stainless steel.

This is for the following reason. That is, the surface of the stainless steel usually has a protective layer for enhancing resistance to acid corrosion, so that when the stainless steel does not contain copper, this protective layer causes a large contact resistance. On the other hand, since copper is included in stainless steel, the resistance of the protective layer is reduced, and as a result, the contact resistance is reduced.

Therefore, by welding copper to the stainless steel constituting the battery case 1, it is possible to omit welding of the battery case 1 and the negative electrode lead 6. In the cylindrical battery (Example 2) in which the negative electrode lead 6 is welded to the battery case 1, even when the welding is broken during use, for example, (1), the internal resistance is kept low.

Although the present invention has been described with reference to preferred embodiments at present, such disclosure should not be construed as limiting. Various modifications and alterations will become apparent to those skilled in the art by reading the foregoing disclosure. Accordingly, it is intended that the appended claims be construed to include all modifications and alterations without departing from the true spirit and scope of the invention.

Industrial availability

The cylindrical battery according to the present invention can be used as a power source for various electronic devices such as portable digital devices.

1 battery case
2 negative plate
3 positive plate
4 separator
5 electrode group
6 cathode leads
7 Positive lead
8 sealing member
9 gaskets
10 intermediate member
11 Disc

Claims (5)

A battery pack comprising: a bottomed cylindrical battery case; an electrode group housed in the battery case together with an electrolyte; a sealing member sandwiched between openings of the battery case; a sealing member interposed between the sealing member and the battery case; Wherein the opening of the battery case is sealed by drawing the opening end of the battery case,
The battery case is made of stainless steel,
The outer diameter of the battery case is 10 mm or less,
Wherein the thickness of the battery case is 0.05 mm or more and 0.2 mm or less. The method according to claim 1,
Wherein the stainless steel constituting the battery case is an austenitic stainless steel. 3. The method according to claim 1 or 2,
Wherein the stainless steel constituting the battery case is a stainless steel having a carbon content of 0.08 mass% or less. 4. The method according to any one of claims 1 to 3,
Wherein the stainless steel constituting the battery case is a stainless steel having a copper content of 1.0 mass% or more and 6.0 mass% or less. 5. The method according to any one of claims 1 to 4,
Wherein the outer diameter of the battery case is 6 mm or less.

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